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27 Mirage + don't work, what 3 blade next?

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Old 06-28-2007, 08:02 PM
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Default 27 Mirage + don't work, what 3 blade next?

326 Concept w/300XS's in case you didn't know from my sig...

I tried 27 Mirage Plus 3 blades a while back. I had to really work the throttle to do any thing and cavitation no matter what. I spun the props to about 3500, laid off them and let the bow drop and then lightly ease in to the throttle to get on plane.


1 person, 200 fuel
5700RPM 69MPH



Nail the throttles to get on plane with drives tucked all the way= cavitation
Nail the throttles to get on plane with drives neutral trim= cavitation
Ease on the throttles to get on plane with drives tucked all the way= cavitation
Ease on the throttles to get on plane with drives neutral trim= cavitation

Cut to the chase- 3 blades will give me the highest top end, what 3 blade should I try next?
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Old 06-28-2007, 08:10 PM
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Did you try a Trophy Plus ? Start with a 25P I know its a 4 Blade, but I have found they work great on the big O/B's
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Old 06-28-2007, 08:17 PM
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Quote:
Originally Posted by CMC View Post
Did you try a Trophy Plus ? Start with a 25P I know its a 4 Blade, but I have found they work great on the big O/B's
Haven't tried that one yet. 13 3/4 diameter- think I should start larger than 25? Here is the rest of my prop testing if that helps..

Four-blade stainless steel design
Unbelievable bow lift and quick planning on outboard-powered bass, flats or sport boats
Delivers superior handling and better control in tight turns with reduced torque and steering loads
For outboards 75 hp and up

Last edited by marylandmark; 06-28-2007 at 08:20 PM.
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Old 06-28-2007, 09:30 PM
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Mark,
It looks to me that you are trying to find a set of props to correct a balance or set-up issue in your boat. It doesn't look like you are likely going to get the balanced/stable ride and top speed you are looking for with this boat as is. As soon as you lift the bow the boat starts to porpoise. This may be because your inter strakes are too short and you are falling off the strakes (balance point) and then to prop is trying to lift again...fall and lift again = porpoise. Conversely the strakes could be too long and the B-1's can't hold the bow because the strakes are pushing it back down.
If you were at Lake X, they would have you first locate the center of gravity (CG). You can do this at a local marina that will lift you boat with a hoist while your boat is in the water. You use one strap and lift the hull just out of the water. You will move the strap fore and aft until you find the CG. You want to have normal weight including passenger, coolers, 50% fuel load, etc. in place. When you are balanced, measure the this point in relation the end of the transom. This gives you the CG of the boat in normal conditions.
From this point, you should have enough info the adjust the bottom to allow the props to work. In the end you will have a better handling boat for your CG and maybe spend less $ than what these numerous sets of props cost.
Maybe Concept would work with you to get the bottom tuned if necessary. Oh, it could also be that your X needs adjusting. Too high for the B-1's to hold the bow?
If it was me, I would tow to St Pete and do in the water testing with Matt at Throttle Up. He can get the set up right. Many of the race teams use Matt's services. You can have a lot of fun and learn a lot going thru this process. If you get lucky, maybe Matt can get you speed and stability with just props.
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Old 06-29-2007, 08:53 AM
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Thanks for the info BenPerfected!

I was hoping props would get all of that done, however this swap-a-prop stuff is getting kind of old...

There is another 326 w/300XS but has a t-top vs. radar arch that is out now in FL- he is testing as well so hopefully I will have some more info to go with soon.
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Old 06-29-2007, 09:11 AM
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Mark,, I suggest you have a conversation with Luis about this ,,, he built the boat , he should know the best way to use it !! Good Luck and keep us informed ,

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Old 06-29-2007, 10:20 AM
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How often to you run WOT??

For only 1-2 mph you might loose I'd test with a bravo 1. Your cruise speeds will be better too.

Also, if you put even a 1/2" spacer in the lowers or lower the bracked down one or two holes you may see a better angle of attack. You'r motors might be mounted too high...

Last edited by Panther; 06-29-2007 at 10:23 AM.
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Old 06-29-2007, 10:29 AM
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I saw in one of the posts on the other thread that one time you ran WOT with zero tab input.

Some boats... not all...if you lift the tabs up all the way it creates a rocker/suction and can actually cause a porpoise. Somtimes you have to run the tabs at a neutral angle so this this doesn't happen.
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Old 06-29-2007, 11:12 AM
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Quote:
Originally Posted by Panther View Post
I saw in one of the posts on the other thread that one time you ran WOT with zero tab input.

Some boats... not all...if you lift the tabs up all the way it creates a rocker/suction and can actually cause a porpoise. Somtimes you have to run the tabs at a neutral angle so this this doesn't happen.
My tabs at 0 are level with the boat.

I run WOT 99% of the time. Leave my dock, idle 1/2 mile, WOT for 8-10 miles, sit and relax, WOT back.

If I want to fish or bar hop it is same story but only 2 miles instead of 8-10.

Suimmary of tested props so far:

24 B1- too small, rev limiter
26 B1- too big
26 B1 labbed- too small
25 QIV-X too much bow lift
25 QIV- still testing
27 M + too small

http://www.offshoreonly.com/forums/s...d.php?t=157298
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Old 06-29-2007, 12:27 PM
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Maybe the motor is up too high then....

Do you have any transducers hanging off the back of the boat, or on the bottom?? My friend just ran into a problem when he mounted his transducer on the transom. It was disrupting the flow of water to his props and was causing it to cavitate getting on plane.
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